I have came across a big box of perfectly fine 2200 mah NiMH at work. I haven’t been able to find much about about using them for an esk8. So my question is what are the downsides to using them, besides the energy density? Also what are some things that I wouldn’t need to worry about vs say lipo’s?
You should test the internal resistance of the cells and see how they do. Also figuring out the model so you can determine their maximum discharge will be handy
You are going to need a lot of batteries In series to get the same voltage as lipos or lions. About double per each cell. Nimh 1.7V
The batteries are 2200Mah, 1.2V in C cell form. They are produced by GP Batteries. So to get say a 12S1P setup I would need (44.4V/1.2V = 37) 37 Batteries in series. Which I believe there may be around 50-60 of them.
@Challlsss I don’t have a multi meter with me at the moment, but can check the resistance when I get the chance.
you could also mount a pair of car or motorcycle batteries on top of the board because you have them… but unless you are trying to recreate the 70lb esk8 of a few years ago - why?
(edit - forgot newer NiMH don’t have typical memory issue)
Bigger issue: Amp delivery (Sag, heat, poor performance/range).
Seriously - 37 in series? at 1p? so you think 1c delivery will work ok for esk8? 2.2Amps might not even turn your motor. (during VESC motor detection i know sometimes i need more than the low start value)
You will need LOTS in parallel to get even 20-30a to really push you along. HUGE SAG.
If you have some spare time and just want to play with it - i get it and have fun, but this will not work well without a huge parallel pack!
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If I had a box of free batteries I would use them to practice welding or soldering fuse wires on.
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the only downside is that they are heavy and dont last as long. other than that a battery is a battery.
I’m not sure i agree and am going to give you a hard time here.
a battery is a battery? So what current in Amps do you consider minimum required to esk8? I would set it reasonably in the 30-40A range - just cruising flats and single motor.
not knowing the actual c rating of the NiMH batteries - i’d bet around 1c, but hope i’m wrong. if 1c(2.2A) 10 x 37 (to get 22A and 12s voltage) = 370 cells!
that’s not a battery, that’s a rolling lead weight! No way you could get it to fit on a normal board.
I see this equivalent to “i found 100 used laptop 18650 batteries and want to make a pack!” discussions. Can you do it with time and testing - sure. But at the end of it you likely have a 20lb battery that barely runs your esk8, and probably overheats the cells and becomes unbalanced quickly. My definition of PITA with time and problems to keep fixing.
Now if you find a steal on some used high drain batteries, test them and group them by tested capacity and resistance… that’s a different story. Building from like tested cells vs a bunch of random cells of poor performance…
Still a lot of work. I’d look on nkon and others for legit quality new cells if you want to go that route.
I’m no custom DIY battery expert - my .02 so YMMV.
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I used to use NiMh in my high current RC car applications and we would flog the shit outa them till they would almost burn up. (But they didnt) For like the last 20 years high torque power tools used nimh before lithium became an option. There are good nimh out there and they could work if you wanted them to.
They arent the best option. Of course it wont be as good as lithium. Thats not the question. The question is can you use them? Answer is yes.
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Yes, I WILL post in a zombie thread, as this is now relevant again.
I’m dying to FLY somewhere with my board, have completely given up on the idea of ever flying with a proper LithiumAnything battery.
So, I’m working on a NiMH travel pack I can take on a plane.
Yes, they self-discharge, have less capacity per weight or volume than LithiumAnything, but are intrinscincly safe and LEGAL to fly with, even in a huge pack.
What’s either changed, or been glossed over is there are GOOD, NIMH cells capable of delivering 25-35C discharge and being charged at 2C+.
I found 5000mAh C cells both indivually and in 6S 7.2V nominal packs for very little money, roughly $22 per 6S pack = $3.66/cell, $220 per pack (as below.)
To duplicate the capacity (at least on paper) of the 36V 10Ah pack in my Evolve Bamboo GT, I’d need 10 packs, 60 cells, in a 30S2P arrangement.
The 6S Turnigy pack has a stated weight of 436g, while the J&Y cell-based “Flylinktech” pack has a stated weight of 375g, making the whole array 4436-3750g (plus interconnects) ~ 8.5-10lbs. This is significantly heavier than even the 300g/8Ah lipo pouch pack I made, but a couple pounds.
The Turnigy packs are listed as 137x47x24mm, while the Flylinktech pack is listed as 134x46x23mm.
The good news is that 10 of these packs fits into an Apache 1800 tactical case from Harbor Freight with room to spare (for a proper BMS, interconnects, charging and output jacks.) I’ve been riding with said 8Ah booster pack for a few weeks, sitting top-side center on my deck, don’t mind it there at all.
Provided I can power the internal BMS with a tiny (legal) internal pack, bet it NiMH or LithiumWhatever, which is needed to fool the controller board into ALLOWING anything but braking to occur, I can power the board with just the external pack.
I plan to build this, will post here when there’s something to show.
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